The secret of Lady Gaga's energy? … “orgasms and spinach". Photograph: Rex Features

If only Mark Ellen had taken his studies a little less seriously and concentrated harder on his career as an aspiring rock musician, the course of modern British history might have taken a very different turn. His fellow members of the Oxford student band Ugly Rumours included a singer named Tony Blair, whose principal qualifications for the role appeared to be boundless ambition and a pair of cowboy boots. "He had a folk-rock look about him – long hair with a fringe – and was keen, organised, quite posh and very funny," Ellen writes, going on to describe the mode of performance the young Blair applied to a repertoire including "Honky Tonk Women", "Johnny B Goode" and "All Right Now": "Low-slung flares, bare midriff, one hand on a hip, the other wagging a cautionary finger, elbows flapping like a chicken."

Blair and Ellen had been introduced by the latter's girlfriend, the 18-year-old Anji Hunter, then completing her sixth-form studies. Ellen first noticed Hunter as she drew applause for singing along to "California Dreamin'" on a pub jukebox with a beer bottle for a microphone, and decided that "she looked like an awful lot of fun". She would go on to become prime minister Blair's gatekeeper – his "other woman", in the headline of an Observer profile in 2001 – and a figure whose backstage power was said to exceed even that of Alastair Campbell.

In those days Hunter's mission was to stop Ellen and his mates spending their days nodding solemnly over albums such as Spirit's Twelve Dreams of Dr Sardonicus and Captain Beefheart's Trout Mask Replica. "Anji was 18 and thought music was designed for singing, jubilation and annoying the neighbours. If it didn't have a practical purpose, forget it. It had never crossed my mind until I met her that Frank Zappa was anything other than a cryptic genius working at the coalface of the avant garde, rather than a hideous dullard who shagged groupies and wrote lewd songs about it. Captain Beefheart was not, apparently, a brave sonic explorer patrolling the outer limits of self-expression but a crashing bore whose music knotted the knees and brought dancefloors to a shuddering halt. Roy Harper … " But we get the point.

Had Ugly Rumours not petered out, imagine the consequences: Tony Blair as Mick Jagger's heir (or, more plausibly, Bono's precursor), with Anji Hunter becoming the music industry's first female super-manager, imperiously guiding the band to global megastardom and a life of palatial dwellings, private jets, charity gigs, exotic holidays and occasional scandals. But if Blair took a different route to a similar destination, Ellen missed out – except for the charity gig, since within a decade his destiny would sweep him into a role as the frontman of the BBC's telecast of Bob Geldof's Live Aid concert, anchoring the 16-hour event for the watching millions ("95% of the world's televisions", supposedly) from a sweltering glass box suspended from the roof of Wembley stadium.

On the road from the dreaming spires to the stadium towers, Ellen had become one of the best-known rock journalists of his generation: a staff writer on the NME, editor of Smash Hits, the co-founder of Q magazine and editor of Select. His notable charm – an engaging combination of impeccable middle-class courtesy and a sharp but seldom malicious wit – also made him a hit as an occasional stand-in for John Peel on Radio 1 and the successor to Bob Harris on The Old Grey Whistle Test. He went on to help launch Mojo magazine and spent several years running a division of a major publishing company before leaving corporate employment to co-found a monthly publication called The Word, a sort of New Yorker for middle-aged former NME readers. Lasting just short of a decade, the magazine fell victim to the printed-word crisis in 2012 and is still mourned by devotees.

Ellen grew up believing that he had been born out of time, a crucial handful of years too late to have been an active participant in the revolution wrought by the Beatles and the Stones but helpless to avoid inheriting its legacy. He would have been at home in the 60s, but the 70s nevertheless gave him plenty to absorb and relate. He is good value on all of it, particularly the colourful home life of the NME, with its permanently warring cast of characters – Nick Kent, Charles Shaar Murray, Julie Burchill, Tony Parsons – whose formidable egos overshadowed the no less talented but more reticent Ellen, ultimately forcing him to seek self-expression elsewhere.

Amid the amusing rock'n'roll slapstick (such as a gruesome description of taking speed with the Teardrop Explodes, the last occasion on which he took drugs, or a detailed account of his attempt, through negotiations of Kissingeresque complexity, to persuade Phil Spector to attend Q's annual awards ceremony), Ellen occasionally sidles up to an important point. Recalling his days of sharing an apartment in Oxford, he writes: "The girls didn't care if a single got scratched or covered in jam as long as you could still dance to it; the boys rarely Hoovered or did any tidying up and yet howled with physical pain if so much as a thumbprint appeared on our copy of Can't Buy a Thrill by Steely Dan." Gender difference in the appreciation and usage of pop music remains a subject unexplored in any real depth, although a world in which girls piled 45s by the Dansette, their paper sleeves wantonly discarded, while boys filed their pristine albums alphabetically has probably been rendered extinct by digital technology.

Full of engaging asides and deft, sometimes unsparing pen-portraits, this autobiographical souffle ends with three passages of unexpectedly disturbing power, in which Ellen glimpses the fate of a form of entertainment that has lost the sense of purpose and proportion it possessed during the years when his own tastes were being formed. He goes on the road in America with U2, whose four members each have a separate limousine to ferry them from the gig to the nearby airport and a waiting Airbus 320 borrowed from the Sultan of Brunei. Then, with The Word on the brink of collapse, he accepts an assignment to interview Lady Gaga for another magazine, and finds himself required to pass an audition before being permitted to put his questions to the singer, who keeps him waiting for several hours, allows him to see her naked, and confides the secret of her energy: "orgasms and spinach". ("It was how I imagined the life of Marilyn Monroe," he writes, "or maybe the court of Marie Antoinette without the ginseng energy drinks.")

Finally he joins Rihanna on a promotional world tour, accompanying the singer's grotesquely swollen entourage of chefs, laser technicians, wardrobe managers, videographers and hospitality liaison executives, and witnessing fellow journalists desperately trying to tweet gossip and photos of the "conflict-free" diamonds included in their goodie bags from the cruising altitude of a customised Boeing 777 fuelled on $300-a-bottle champagne and other mood-enhancing substances. It is a tribute to Ellen's resilience that not even this sensory assault can erode the powers of humour and observation that make his book so enjoyable.